Invasive Africanized honeybees change the structure of native pollination networks in Brazil
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The Africanized honeybee Apis mellifera (AHB) is an invasive species spread over all Brazilian biomes, which has negative impacts on native bee populations, but whose impacts on native plants are still controversial. In order to understand how its impacts extend to the pollination service at the community level, we studied the AHB and its interactions in a multi-species context using network theory. We analyzed six pollination networks from the Brazilian Caatinga, a xeric biome where beekeeping is increasing very quickly. The AHB occupied a central position in all networks, as it was responsible for a large share of the interactions observed (14 ± 7 %) and bound together different modules. By simulating the removal of the AHB from each network, we observed no effects on connectance, but a strong decrease in nestedness (−23 ± 19 %) and an increase in modularity (8 ± 5 %). The robustness of networks to cumulative random extinctions was on average not affected. In summary, our evidence points out that the AHB induces significant changes in the structure of native pollination networks, mainly by making them more cohesive and monopolizing many interactions. Although the AHB did not affect network robustness, its net impact on the pollination service may be negative, because this invasive species is very generalistic and may not be an efficient pollinator for some native plants.
KeywordsApis mellifera Complex networks Ecosystem services Centrality Modularity Nestedness Pollination
D. Vázquez and P. R. Guimarães Jr. made invaluable suggestions for the manuscript. C. Dormann, F. M. D. Marquitti, M. Almeida-Neto, N. Blüthgen, P. R. Guimarães Jr. and R. Guimerà helped us use their network software. F. França, E. Melo and M. R. V. Barbosa identified plant species. J. Ollerton helped us with literature on the impacts of invasive honeybees. This work was funded with grants from the Brazilian Research Council (CNPq) and the Research Foundation of Bahia (FAPESB). GMMS (309711/2009-6), F.C.V.Z. (501850/2009-0) and CFM (307687/2008-2) received research productivity fellowships from CNPq. MARM received a postdoctoral fellowship from the Alexander von Humboldt Foundation (1134644).
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